PowerPoint Presentation

[Audio] Welcome to the narrated presentation on Shallow Sewer System. The conventional sewerage system, besides requiring huge capital investment, is often found to encounter unreasonable delay in its implementation. A group of professionals at NCPE, with over two decades of experience in the field of water supply and sewerage, have undertaken a pilot study in one sewerage zone of Nalgonda Municipality in Telangana, in order to demonstrate that the shallow sewer system is cost effective, permits rapid implementation, causes least public nuisance and involves minimum road digging – a perfect recipe for the success of the alternative sewerage system..

[Audio] More than 400 million Urban population of India is spread across 4000 ULBs. Urban roads are known to span over 8 lakhs kilometers, half of which are CC and BT roads. Only 40 thousand Kilometers of the road network is covered with underground sewerage system.

[Audio] It is a herculean task to implement conventional sewerage system in the uncovered urban areas in order to meet the Service Level Benchmarks. While an estimated amount of rupees 3 lakh crore is required to lay the sewer line, a whopping amount of rupees 2 lakh crore is likely to be required for restoration of the dug roads. Most of the ULBs in the country can ill afford such a huge capital investment. In this scenario, the shallow sewer system may turn out to be the panacea for the urban sewerage solution..

[Audio] In the absence of underground sewerage system, open drains conveying sullage are liable to spread diseases, contaminate water sources, serve as breeding sites to mosquitoes, cause water logging and damage roads when they overflow..

[Audio] Larger municipalities avoid the unsightliness and public nuisance by adopting the conventional underground sewerage system in order to overcome the hazards of open drains. A brief review of the conventional system is presented in the next few slides..

[Audio] In the Conventional Sewerage System, very often, the sewer pipes are laid in the middle of the road with manholes at regular interval of 30 meter centre to centre. Traditionally, the sewer network consists of lateral sewer, branch sewer, main sewer or outfall sewer. The house service connection is made to the nearest manhole through an inspection chamber using a 100 mm or 150 mm diameter pipe..

[Audio] The conventional sewerage system is based on well established design guidelines and is known for convenience, low health risk, no smell and disease vectors and universal application in the sense that it is suitable for all types of wastes, including industrial waste. However, the conventional system is not without its disadvantages..

[Audio] The most significant restrictive aspects of the conventional sewerage system are its high capital cost, deep excavation and extensive road damage. Also, the system is difficult to implement in high density areas and in areas with narrow roads. In many cases, it takes several years to commission the system through out the city. Due to its intrinsic structure, the system is not easily amenable to extension to new areas. All these factors weigh negatively on the minds of municipal decision makers while making a choice of sewerage system..

[Audio] Since the sewers run mostly under gravity, provision of adequate gradient is necessary in order to attain the self cleansing velocity. In some instances, the topography of the area and requirement of gradient leads to large depths even for small sewer diameters like 200 mm. Based on the depth, the manhole size becomes very large in comparison to the pipe size. The resulting excavation obstructs pedestrian and vehicular traffic due to which the residents are put to untold hardship for several weeks..

[Audio] The damage to roads, specially narrow roads, is so extensive that restoration in the form of patch work is not at all satisfactory. Apart from subsidence, the patch is also susceptible to potholes during monsoon rains. Hence, it is necessary to re-carpet the entire width of the road. This aspect of conventional sewerage scares the policy makers to such an extent that they develop second thoughts about adopting it in their municipality..

[Audio] The less said about the manhole covers, the better. In the absence of strict quality control measures, the contractors fail to comply with the execution norms due to which there is subsidence in the filling and the manhole cover is not flush with the road surface. Such a scenario leads to accidents, specially during night times, in areas lacking in adequate street lighting. As an Independent Review and Monitoring Agency, NCPE has witnessed this is several projects..

[Audio] The Municipal commissioners find themselves between the devil and the deep sea with respect to sewerage system; the choice between unhygienic open drains and the laboriousness of the conventional sewerage system is hard to make. In this scenario, the Municipal Commissioner of Nalgonda Municipality has requested NCPE to propose an economical, practical, low maintenance solution while avoiding damage to the roads and causing minimum disturbance to the public. NCPE has proposed the shallow depth sewerage system as it addresses all the requirements of the ULB..

[Audio] The shallow sewerage system, while being deep enough to receive flows from contributing households, it is located such that the depth is minimum. Smaller Pipe diameter, shallower burial, narrower construction corridor and lack of manholes makes shallow sewerage system a low cost alternative. When built with CPVC pipe, it can be easily flexed so that curvilinear routing becomes easy. It can be laid at a flatter gradient as no minimum flow velocity needs to be maintained..

[Audio] The shallow sewer system is permitted in the CPHEEO Manual under decentralized sewerage system. In 2018, the Government of Andhra Pradesh has successfully implemented it in many ULBs. It is reported that the system is working satisfactorily since then. As the depth is shallow, the system has to be built away from heavy vehicular loads. In Indian scenario, it is possible to lay the sewers along the property line or beneath the sidewalks..

[Audio] The pipeline can be encased in concrete when the depth is less than 0.8 m and it is subjected to vehicular loads. Since the construction corridors are narrow, the system can be easily implemented into the built environment. The maximum spacing of inspection chambers is 40 m c/c. Besides this, one chamber is provided for each house service connection, at each sewer junction, at each change in direction and for cleaning and maintenance.

[Audio] The shallow sewer system can be implemented at a lower capital and operating cost than conventional sewers The capital cost is lowered due to reduced excavation, no road cutting and restoration, lack of manholes etc. The maintenance cost is also low as the shallow depth makes maintenance easy and cheap As the manhole depth is not more than 1.1 m, house connections and block sewers can be easily maintained by the community by adopting cheap rodding devices. This reduces the sewerage tariff..

[Audio] The shallow sewerage system is designed for one of the sewerage zones of Nalgonda Municipality. Both conventional and shallow sewer designs are attempted in order to bring out the cost difference between the two systems. As per CPHEEO norms, 85 percent of the water supplied is taken as the sewage quantity for design purpose..

[Audio] The first step in the design of sewerage system is to produce the topographic map, road network map and contour map. These maps are produced by undertaking DGPS and total station survey. The X, Y Z, coordinates are plotted using a suitable software resulting in the three maps. Subsequently, the catchment map and sewerage zone map are also produced..

[Audio] The design of the sewer network is done using sewerGEMS software using standard design parameters as recommended by CPHEEO in the Manual. For the design of shallow sewer network, the UNCHS Habitat guidelines contained in ' Design of Shallow Sewer System', are employed along with the CPHEEO guidelines. The total length of the sewer network is 84.243 Km and the project cost is Rs. 158.03 crore..

[Audio] In the design of shallow sewer system, sewers with burial depths of up to 1.1 m qualify as shallow sewers. All the remaining sewers are either sub-mains or mains and are designed as conventional sewers. Two sewers of 100 mm diameter are laid, one on each side of the road, along the property line, at a slope of 1 in 167 as recommended in the UNCHS manual. Each connection is provided with an inspection chamber. The total project cost is obtained as Rs. 90.64 lakhs. Cost comparison with the conventional system indicates that there is a 42.64 percent overall saving. The expenditure is 13 percent excess in laying of sewers owing to the dual pipes but this is meager in compassion to the 82.65 percent saving in the road restoration works..

[Audio] NCPE believes that the shallow sewer system in combination with the conventional system can prove to be a game changer in the sanitation sector. Thank You..